In electrostatographic image forming apparatus, toner images are formed on the surface of a toner image bearing member (TIBM) and then transferred to a receiving sheet. One known approach to transferring a toner image to a receiving sheet is to place the receiving sheet between the image member and a transfer member, for example, a transfer roller. The transfer roller is biased to create an electric field urging the toner toward the sheet and also helps maintain intimate contact between the sheet and the toner image.
Transfer rollers thus have been used in electrostatographic copiers and printers to move toner particles on the photoconductor web to sheets of paper, transparencies or other medium. This is done by charging the medium with opposite polarity charges to that of toner.
Tackdown rollers are used in color electrostatographic copiers or printers to electrostatically tack down the sheets of paper or other medium to a transport web. The tack down function is accomplished by charging up the paper with opposite charges to that of the web. These rollers serve as a charger and they also "iron" out air pockets between the paper and the transport web.
Alternatively, the tackdown roller function can be accomplished by an uncharged capture roller which will iron down the paper to the web removing air pockets and ensuring the delivery of the sheets to a corona charger which then tacks down the sheets to a transport web. The transport web moves the sheets of paper through the separate color engines.
In the above applications, the photoconductor web or transport web will have a splice seam where toner particles can collect due to the physical discontinuities in the surface at the seam. Cleaning methods for these webs are not effective in completely removing all the toner from the splice. As the splice seam passes by the above rollers, some toner particles are transferred to the roller surface. The scam contamination then transfers to the sheets passing by the rollers generating line artifacts.
In color applications with a transport web, toner collected from the splice seam can be redeposited onto the web surface and to the imaging side of the incoming sheets passing by the roller. In the transfer roller applications, the artifact shows up on backsides of copies. Toner splice artifacts can occur multiple times within a sheet of paper.
The transfer of toner particles from the splice to the roller can occur in either metallic rollers or in compliant rollers with urethane blankets. Methods such as reverse biasing to prevent toner pick up are not always effective to completely eliminate the artifacts and they are generally expensive to implement. Other attempts to smooth the web splice do not completely eliminate toner collected there. A combination of reverse bias with an active cleaner and coatings on the roller to reduce the roller surface energy can be used which increases the cost and drag torque on the roller.
The presence of a splice seam on the web may need to be monitored to avoid imaging over it since artifacts can be produced on both sides of the sheets. An improvement in this regard is disclosed in U.S. application Ser. No. 09/199,896, filed Nov. 25, 1998, now U.S. Pat. No. 6,016,415.
In applications where the roller has a compliant blanket such as urethanes and when there might be high pressure contact, a compression set can be impressed on the roller when parked for extended periods of time against a hard backup roller. In these applications, it is desirable to articulate the roller away from the hard back up roller to avoid the formation of a compression set. The articulation means are costly and it occupies premium space in the overall design of the copiers.
A simple solution to the above problems that will prevent the transfer of toner particles from a seam formed by the splice to a transfer, tackdown or capture roller and thus avoid or reduce the generation of artifacts on copies would be highly desirable.